Method for making integrated circuit device

ABSTRACT

A method for making an integrated circuit device by: forming a plurality of transistors on a semiconductor substrate; forming multilayer interconnects by depositing a layer of metal; patterning the metal layer; depositing a first dielectric material, depositing a second dielectric material, patterning the first and second dielectric materials; and depositing a via filling metal material into the patterned areas; or, alternatively, by forming transistors on a substrate; depositing one of an electrically insulating or electrically conducting material; patterning said one of an electrically insulating or electrically conducting material; and depositing the other of the electrically insulating or electrically conducting material, so as to form a layer over said transistors having both electrically insulating and electrically conducting portions; wherein the first dielectric material, which is an organosiloxane material, and the electrically insulating material each has a carbon to silicon ratio of 1.5 to 1 or more.

This application is a division of application Ser. No. 11/215,303, filedAug. 31, 2005, which claims priority of U.S. Provisional Applicationsfor Patent Ser. Nos. 60/605,553 filed Aug. 31, 2004, and 60/644,304filed Jan. 18, 2005, which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to thin films suitable as dielectrics inIC's and for other similar applications. In particular, the inventionconcerns thin films comprising compositions obtainable by polymerizationof silicon containing monomers, which yield an at least partiallycross-linked siloxane structure. The invention also concerns a methodfor producing such films by preparing siloxane compositions bypolymerization of the monomers, by applying the polymerized compositionson a substrate in the form of a layer and by curing the layer to form afilm. Further, the invention concerns integrated circuit devices andmethods of manufacturing them.

2. Description of Related Art

Built on semiconductor substrates, integrated circuits comprise millionsof transistors and other devices, which communicate electrically withone another and with outside packaging materials through multiple levelsof vertical and horizontal wiring embedded in a dielectric material.Within the metallization structure, “vias” make up the vertical wiring,whereas “interconnects” form the horizontal wiring. Fabricating themetallization can involve the successive depositing and patterning ofmultiple layers of dielectric and metal to achieve electrical connectionamong transistors and to outside packaging material. The patterning fora given layer is often performed by a multi-step process comprisinglayer deposition, photoresist spin, photoresist exposure, photoresistdevelop, layer etch, and photoresist removal on a substrate.Alternatively, the metal may sometimes be patterned by first etchingpatterns into a layer of a dielectric material, filling the pattern withmetal, then subsequently chemically/mechanically polishing the metal sothat the metal remains embedded only in the openings of the dielectric.As an interconnect material, aluminum has been utilized for many yearsdue to its high conductivity, good adhesion to SiO₂, known processingmethods (sputtering and etching) and low cost. Aluminum alloys have alsobeen developed over the years to improve the melting point, diffusion,electromigration and other qualities as compared to pure aluminum.Spanning successive layers of aluminum, tungsten has traditionallyserved as the conductive via plug material.

In IC's, silicon dioxide, having a dielectric constant of around 4.0,has been the dielectric of choice, used in conjunction withaluminum-based and tungsten-based interconnects and via for many years.

The drive to faster microprocessors and more powerful electronic devicesin recent years has resulted in very high circuit densities and fasteroperating speeds which—in turn—have required that higher conductivitymetals and significantly lower-k dielectrics compared to silicon dioxide(preferably below 3.0) be used. In the past few years, VLSI (and ULSI)processes have been moving to copper damascene processes, where copper(or a copper alloy) is used for the higher conductance in the conductorlines and a spin-on or CVD process is used for producing low-kdielectrics which can be employed for the insulating materialsurrounding the conductor lines. To circumvent problems with etching,copper along with a barrier metal is blanket deposited over recesseddielectric structures consisting of interconnect and via openings andsubsequently polished in a processing method known as the “dualdamascene.” The bottom of the via opening is usually the top of aninterconnect from the previous metal layer or, in some instances, thecontacting layer to the substrate.

Summarizing: aside from possessing a low dielectric constant, the idealdielectric should have the following properties:

1. High modulus and hardness in order to bind the maze of metalinterconnects and vias together in particular in the final chippackaging step as well as abet chemical mechanical polishing processingsteps.

2. Low thermal expansion, typically less than or equal to that of metalinterconnects.

3. Excellent thermal stability, generally in excess of 400° C., but moreoften even better than 500° C.

4. No cracking even as thick films structures, excellent fill andplanarization properties.

5. Excellent adhesion to dielectric, semiconductor, diffusion barrierand metal materials.

6. Sufficient thermal conductivity to dissipate joule heating frominterconnects and vias.

7. Material density that precludes absorption of solvents, moisture, orreactive gasses.

8. Allows desired etch profiles at very small dimensions.

9. Low current leakage, high breakdown voltages, and low loss-tangents.

10. Stable interfaces between the dielectric and contacting materials.

By necessity, low-k materials are usually engineered on the basis ofcompromises.

Organic polymers can be divided into two different groups with respectto the behavior of their dielectric constant. Non-polar polymers containmolecules with almost purely covalent bonds.

Since they mainly consist of non-polar C—C bonds, the dielectricconstant can be estimated using only density and chemical composition.Polar polymers do not have low loss, but rather contain atoms ofdifferent electronegativity, which give rise to an asymmetric chargedistribution. Thus polar polymers have higher dielectric loss and adielectric constant, which depends on the frequency and temperature atwhich they are evaluated. Several organic polymers have been developedfor dielectric purposes. However, applicability of these films islimited because of their low thermal stability, softness, andincompatibility with traditional technological processes developed forSiO₂ based dielectrics.

Therefore most of the current developments are focusing on SSQ(silsesquioxane or siloxane) or silica based dielectric materials. ForSSQ based materials, silsesquioxane (siloxane) is the elementary unit.Silsesquioxanes, or T-resins, are organic-inorganic hybrid polymers withthe empirical formula (R—SiO_(3/2))_(n). The most common representativeof these materials comprise a ladder-type structure, and a cagestructure containing eight silicon atoms placed at the vertices of acube (T₈ cube) on silicon can include hydrogen, alkyl, alkenyl, alkoxy,and aryl.

Many silsesquioxanes have reasonably good solubility in common organicsolvents due to their organic substitution on Si. The organicsubstitutes provide low density and low dielectric constant matrixmaterial. The lower dielectric constant of the matrix material is alsoattributed to a low polarizability of the Si—R bond in comparison withthe Si—O bond in SiO₂. The silsesquioxane based materials formicroelectronic application are mainly hydrogen-silsesquioxane, HSQ, andmethyl-silsesquioxane, (CH₃—SiO_(3/2))_(n) (MSQ). MSQ materials have alower dielectric constant as compared to HSQ because of the larger sizeof the CH₃ group ˜2.8 and 3.0-3.2, respectively and lower polarizabilityof the Si—CH₃ bond as compared to Si—H.

The silica-based materials have the tetrahedral basic structure of SiO₂.Silica has a molecular structure in which each Si atom is bonded to fouroxygen atoms. Each silicon atom is at the center of a regulartetrahedron of oxygen atoms, i.e., it forms bridging crosslinks. Allpure of silica have dense structures and high chemical and excellentthermal stability. For example, amorphous silica films, used inmicroelectronics, have a density of 2.1 to 2.2 g/cm³. However, theirdielectric constant is also high ranging from 4.0 to 4.2 due to highfrequency dispersion of the dielectric constant which is related to thehigh polarizability of the Si—O bonds. Therefore, it is necessary toreplace one or more Si—O—Si bridging groups with C-containing organicgroups, such as CH₃ groups, which lowers the k-value. However, theseorganic units reduce the degrees of bridging crosslinks as wellincreases the free volume between the molecules due to steric hindrance.Therefore, their mechanic strength (Young's modulus <6 GPa) and chemicalresistance is reduced compared to tetrahedral silicon dioxide. Also,these methyl-based silicate and SSQ (i.e., MSQ) polymers have relativelylow cracking threshold, typically on the order of 1 um or less.

Quite recently there have been some efforts to develop enhanced MSQpolymers by co-polymerizing them with disilanes, i.e.,bistrimethoxysilane, that contain bridging alkyl groups between silanesand thus crosslinking density has been increased. However, thesematerials still contain significant amount of methyl-based silanes, i.e.methyl-trimethoxysilane, as comonomers and due to methyl co-polymernature only moderate Young's modulus and hardness properties has beenobtained, with dielectric constant of around 2.93.

SUMMARY OF THE INVENTION

It is an object of the present invention to eliminate the problems ofthe known technical solutions and to provide novel thin films, whichhave excellent mechanical and thermal properties.

It is another object of the invention to provide dielectric layers onsilicon wafers.

It is a third object of the invention to provide methods of producingpoly(organo siloxane) compositions which are suitable for thepreparation of thin films having excellent dielectric properties.

It is a still a fourth object of the invention to provide a method ofpatterning dielectric films in semiconductor devices.

These and other objects, together with the advantages thereof over theknown dielectric thin films and methods for the preparation thereof,which shall become apparent from specification which follows, areaccomplished by the invention as hereinafter described and claimed.

In order to achieve these objectives in the present invention, weintroduce a multisilane molecule based polyorgano silsesquioxanematerial for an interlayer insulating film for a semiconductor device.The polymer is based on one precursor molecule and no co-monomers areapplied.

Generally, the monomer comprises two metal atoms which areinterconnected by a bridging hydrocarbyl radical and which exhibithydrolysable substitutents on both of the metal atoms along with atleast one organic group which is capable of reducing the polarizabilityof the polymer formed from the monomer. In particular, the metal atomsare silicon atoms, and the bridging radical is a linear or branchedhydrocarbyl group which links the two silicon atoms together.Furthermore, one of the silicon atoms contains three hydrolysable groupsand the other silicon atom contains two hydrolysable groups and apolarizability reducing organic group, such as an alkyl, an alkenyl oran aryl organic group. The latter group may be fully or partiallyfluorinated.

The general formula I of the precursor used in the present invention isthe following:

wherein:

-   -   R₁ is a hydrolysable group, such as a halide, an alkoxy or an        acyloxy group,    -   R₂ is a polarizability reducing organic group, such as an alkyl,        alkenyl or aryl group, and    -   R₃ is a bridging group, in particular a (bivalent) linear or        branched hydrocarbyl group.

The polymer of the present innovation is formed by hydrolysing thehydrolysable groups of the multisilane monomer and then furtherpolymerising it by a condensation polymerisation process.

The new material can be used as a low k dielectric film in an objectcomprising e.g. a (silicon) wafer.

The present invention also provides a method of forming a thin filmhaving a dielectric constant of 3.0 or less, comprising homopolymerizinga monomer having the formula I, to form a siloxane material, depositingthe siloxane material in the form of a thin layer; and curing the thinlayer to form a film.

Finally, the invention provides a number of alternative embodiments formaking integrated circuit devices of a kind, which comprises a pluralityof transistors on a semiconductor substrate and having multilayerinterconnects. The multilayer interconnects are formed by depositing alayer of metal, patterning the metal layer, depositing a firstdielectric material having a first modulus and a first k value,depositing a second dielectric material having a second modulus higherthan the first modulus of the first material and with a k value lowerthan the first k value of the first material, and—without performingchemical mechanical planarization—patterning the first and seconddielectric materials and depositing a via filling metal material intothe patterned areas. The first dielectric material preferably comprisesa material according to claim 1.

More specifically, the new materials according to the present inventionare characterized by what is stated in the characterizing part of claim1.

The object according to the invention is characterized by what is statedin the characterizing part of claim 18 and the method of forming a thinfilm having a dielectric constant of 2.9 or less by what is stated inthe characterizing part of claim 19.

The methods of making integrated circuit devices are characterized bywhat is stated in claims 28 and 29, and the integrated circuit devicesby what is stated in claim 32.

Considerable advantages are obtained by the present novel materials andby the methods of manufacturing them. Thus, the present inventionpresents a solution for existing problems related to low-k dielectricpolymers, more specifically mechanical properties (modulus andhardness), cracking threshold and thermal properties, especiallyapplicable for aluminum reflow processing temperatures (also known ashot aluminum process). At the same time, the present invention providesexcellent chemical resistance and very low chemical adsorption behaviordue to high cross-linking bridging group density.

Another important advantages is that the novel low-k dielectricmaterials have excellent properties of planarization resulting inexcellent local and global planarity on top a semiconductor substratetopography, which reduces or even fully eliminates the need for chemicalmechanical planarization after dielectric and oxide liner deposition.

Furthermore, the novel materials have excellent gap fill properties.

Next, the invention will be examined more closely by means of thefollowing detailed description and with reference to a number of workingexamples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the FT-IR spectrum of the polymer prepared in Example 1;

FIG. 2 a shows in cross-section a tungsten via processed in accordancewith the present invention; and

FIG. 2 b shows in cross-section a via formed by a hot aluminum process.

DETAILED DESCRIPTION OF THE INVENTION

The present innovation provides a low dielectric constant siloxanepolymer applicable for forming thermally and mechanically stable, highcracking threshold, dense and low pore volume and pore size dielectricfilm. The polymer results in water and silanol free film with excellentlocal and global planarization as well as gap fill after subjected tothermal treatment with having excellent electrical properties. A filmmade out of the invented polymer remains structurally, mechanically andelectrically unchanged after final cure even if subjected totemperatures higher than the final cure temperature. All theseproperties, as they are superior over conventional low dielectricconstant polymers, are crucial to overcome existing problems in lowdielectric constant film integration to a semiconductor device.

The present innovation provides a homogeneous low dielectric constantpolymer comprising only one component multisilane mononer unit with atleast one organic bridging group between silicon atoms. In addition, oneof the silicon atoms also contains one polarizability reducing group,such as an alkyl, alkylene or aryl organic group. One of the siliconatoms comprises two hydrolysable groups and the other three hydrolysablegroups capable of forming a continuous siloxane backbone matrix oncehydrolyzed and polymerized, such as halide, alkoxy or acyloxy groups,but most preferably chlorine groups.

The general formula I of the precursor used in the present invention isthe following:

wherein:

-   -   R₁ is a hydrolysable group    -   R₂ is a polarizability reducing organic group, and    -   R₃ is a bridging group, in particular a linear or branched        hydrocarbyl residue.

R₁ is preferably selected from the group of halides, alkoxy groups andacyloxy groups, R₂ is preferably selected from alkyl groups, alkenylgroups and aryl groups, and R₃ is preferably selected from linear andbranched alkylene groups, alkenylene groups and alkynylene groups.

The cured composition obtained by essentially homopolymerizing monomersof the above formula, with subsequent curing to achieve cross-linking,comprises a cross-linked organosiloxane polymer, i.e.poly(organosiloxane). It can be formed into a thin film.

‘Alkenyl’ as used herein includes straight-chained and branched alkenylgroups, such as vinyl and allyl groups. The term ‘alkynyl’ as usedherein includes straight-chained and branched alkynyl groups, suitablyacetylene. ‘Aryl’ means a mono-, bi-, or more cyclic aromaticcarbocyclic group, substituted or non-substituted; examples of aryl arephenyl and naphthyl. More specifically, the alkyl, alkenyl or alkynylmay be linear or branched.

Alkyl contains preferably 1 to 18, more preferably 1 to 14 andparticularly preferred 1 to 12 carbon atoms. The alkyl is preferablybranched at the alpha or beta position with one and more, preferablytwo, C₁ to C₆ alkyl groups, especially preferred halogenated, inparticular partially or fully fluorinated or per-fluorinated alkyl,alkenyl or alkynyl groups. Some examples are non-fluorinated, partiallyfluorinated and per-fluorinated i-propyl, t-butyl, but-2-yl,2-methylbut-2-yl, and 1,2-dimethylbut-2-yl. In particular, the alkylgroup is a lower alkyl containing 1 to 6 carbon atoms, which optionallybears 1 to 3 substituents selected from methyl and halogen. Methyl,ethyl, n-propyl, i-propyl, n-butyl, i-butyl and t-butyl are particularlypreferred.

Alkenyl contains preferably 2 to 18, more preferably 2 to 14 andparticularly preferred 2 to 12 carbon atoms. The ethylenic, i.e. twocarbon atoms bonded with double bond, group is preferably located at theposition 2 or higher, related to the Si or M atom in the molecule.Branched alkenyl is preferably branched at the alpha or beta positionwith one and more, preferably two, C₁ to C₆ alkyl, alkenyl or alkynylgroups, particularly preferred fluorinated or per-fluorinated alkyl,alkenyl or alkynyl groups.

Alkynyl contains preferably 3 to 18, more preferably 3 to 14 andparticularly preferred 3 to 12 carbon atoms. The ethylinic group, i.e.two carbon atoms bonded with triple bond, group is preferably located atthe position 2 or higher, related to the Si or M atom in the molecule.Branched alkynyl is preferably branched at the alpha or beta positionwith one and more, preferably two, C₁ to C₆ alkyl, alkenyl or alkynylgroups, particularly preferred per-fluorinated alkyl, alkenyl or alkynylgroups.

The aryl group is preferably phenyl, which optionally bears 1 to 5substituents selected from halogen, alkyl or alkenyl on the ring, ornaphthyl, which optionally bear 1 to 11 substituents selected fromhalogen alkyl or alkenyl on the ring structure, the substituents beingoptionally fluorinated (including per-fluorinated or partiallyfluorinated).

“Hydrolysable group” stands for halogen (chlorine, fluorine, bromine),alkoxy (in particular C₁₋₁₀ alkoxy, such as methoxy, ethoxy, propoxy, orbutoxy), acyloxy or any other group that can easily be cleaved off themonomer during polymerization, e.g. condensation polymerization.

The alkoxy groups stand generally for a group having the formula R₄O—,wherein R₄ stands for an alkyl as defined above. The alkyl residue ofthe alkoxy groups can be linear or branched. Typically, the alkoxygroups are comprised of lower alkoxy groups having 1 to 6 carbon atoms,such as methoxy, ethoxy and t-butoxy groups.

The acyloxy groups have the general formula R₅O₂—, wherein R₅ stands foran alkyl as defined above. In particular, the alkyl residue of theacyloxy group can have the same meanings as the corresponding residue inthe alkoxy group.

In the context of the disclosure the organic group substituent halogenmay be a F, Cl, Br or I atom and is preferably F or Cl. Generally, term‘halogen’ herein means a fluorine, chlorine, bromine or iodine atom.

In the monomer of formula I, the silicon atoms are linked to each othervia a linker group. Typically, the linker comprises 1 to 20, preferablyabout 1 to 10, carbon atoms. Examples of suitable linker groups R₃include alkylene, alkenylene and alkynylene groups. “Alkylene” groupsgenerally have the formula —(CH₂)_(r)— in which r is an integer 1 to 10.One or both of the hydrogens of at least one unit —CH₂— can besubstituted by any of the substituents mentioned below. The “alkenylene”groups correspond to alkylene residues, which contain at least onedouble bond in the hydrocarbon backbone. If there are several doublebonds, they are preferably conjugated. “Alkynylene” groups, by contrast,contain at least one triple bond in the hydrocarbon backbonecorresponding to the alkylene residues.

The bivalent linker residue can be unsubstituted or substituted. Thesubstitutents are preferably selected from the group of fluoro, bromo,C₁₋₁₀-alkyl, C₁₋₁₀-alkenyl, C₆₋₁₈aryl, acryl, epoxy, carboxyl andcarbonyl groups. A particularly interesting alternative is comprised ofmethylene groups substituted with at least one alkyl group, preferably alower alkyl group or 1 to 4 carbon atoms. As a result of thesubstitution, a branched linker chain is obtained. The branched linkerchain, e.g. —CH(CH₃)— can contain in total as many carbon atoms as thecorresponding linear, e.g. —CH₂CH₂—, even if some of the carbon atomsare located in the side chain, as shown below in connection with theworking examples. Such molecules can be considered “isomeric”, for thepurpose of the present invention.

As examples of a particularly preferred compounds according to formulaI, 1-(trichlorosilyl)-2-(methyldichlorosilyl)ethane and1-(Methyldichlorosilyl)-1-(trichlorosilyl) ethane can be mentioned.

The present invention provides a low dielectric constant siloxanepolymer applicable for forming thermally and mechanically stable, highcracking threshold, dense and low pore volume and pore size dielectricfilm. The polymer results in water and silanol free film with excellentlocal and global planarization as well as gap fill after subjected tothermal treatment with having excellent electrical properties. A filmmade out of the invented polymer remains structurally, mechanically andelectrically unchanged after final cure even if subjected totemperatures higher than the final cure temperature. All theseproperties, as they are superior over conventional low dielectricconstant polymers, are crucial to overcome existing problems in lowdielectric constant film integration to a semiconductor device.

The polymerization synthesis is based on hydrolysis and condensationchemistry synthesis technique. Polymerization can be carried out in meltphase or in liquid medium. The temperature is in the range of about 20to 200° C., typically about 25 to 160° C., in particular about 80 to150° C. Generally polymerization is carried out at ambient pressure andthe maximum temperature is set by the boiling point of any solvent used.Polymerization can be carried out at refluxing conditions. It ispossible to polymerize the instant monomers without catalysts or byusing alkaline or, in particular, acidic catalysts.

The present organosiloxane materials have a (weight average) molecularweight of from 500 to 100,000 g/mol. The molecular weight can be in thelower end of this range (e.g., from 500 to 10,000 g/mol, or morepreferably 500 to 8,000 g/mol) or the organosiloxane material can have amolecular weight in the upper end of this range (such as from 10,000 to100,000 g/mol or more preferably from 15,000 to 50,000 g/mol). It may bedesirable to mix a polymer organosiloxane material having a lowermolecular weight with a organosiloxane material having a highermolecular weight.

We have found that a suitable polymer composition can be obtained byhomopolymerizing a monomer of formula I comprising either a linear or abranched linker group.

However, it is also possible to obtain suitable compositions bycopolymerizing a first monomer having formula I, wherein R₃ stands for afirst hydrocarbyl residue, with a second monomer having formula I,wherein R₃ stands for a second hydrocarbyl residue, said first andsecond hydrocarbyl residues being different. This will allow fortailoring of the mechanical and electrical properties of thecomposition. The disclosed embodiment comprises the option ofcopolymerizing a first monomer having formula I, wherein R₃ stands for alinear hydrocarbyl residue, with a second monomer having formula I,wherein R₃ stands for a branched hydrocarbyl residue, the molar ratio ofthe first monomer to the second monomer is 95:5 to 5:95, in particular90:10 to 10:90, preferably 80:20 to 20:80. Another alternative is tocopolymerize a first monomer having formula I, wherein R₃ stands formethylene, with a second monomer having formula I, wherein R₃ stands fora hydrocarbyl residue having at least 2, preferably 2 to 6 carbon atoms.In that alternative, the molar ratio of the first monomer to the secondmonomer is 50:50 to 0.1:99.9, in particular 30:80 to 1:99, preferably20:80 to 5:95. Preferably, the second monomer comprises a hydrocarbylresidue selected from ethylene, propylene, i-propylene, and n-, i- andt-butylene. The advantages of copolymerizing two different kinds ofmonomers of formula I will be discussed in more detail below.

As will appear from below, thin films having excellent properties can beobtained by polymerizing1-(trimethoxysilyl)-2-(methyldichlorosilyl)ethane,2,2,4,4,4-pentachloro-2,4-disilabutane, or2,2,4,4,4-pentamethoxy-2,4-disilabutane.

Other interesting materials can be obtained by co-polymerizing1-(trichlorosilyl)-2-(methyldichlorosilyl)ethane and2,2,4,4,4-pentachloro-2,4-disilabutane, or1-(trimethoxysilyl)-2-(methyldichlorosilyl)ethane and2,2,4,4,4-pentamethoxy-2,4-disilabutane.

According to one preferred embodiment, in order to modify theproperties, the siloxane material deposited on a substrate of asemiconductor device is heated to cause further cross-linking, whereby afilm is obtained, having a shrinkage after heating of less than 10%,preferably less than 5%, in particular less than 2%, and a thermalstability of more 425° C.

The polymer of the present invention is capable of forming lowdielectric films having a dielectric constant of 3.0 or less, inparticular 2.9 or less, preferably about 2.5 to 1.9, a Young's modulusof at least 8.0, preferably 10.0 GPa or more, a porosity of 5% or lessand cracking threshold of 2 um or more after subjected to thermaltreatment. Also the film formed from the polymer using a multisilanecomponent remains stable on a semiconductor structure at temperatures upto 500° C. or more after subjecting the film for thermal treatment at450° C. or less for 1 hour or less.

As mentioned above, the present invention also provides methods ofproducing integrated circuit devices. Such methods typically comprisethe steps of:

-   -   forming a plurality of transistors on a semiconductor substrate;    -   forming multilayer interconnects by:        -   depositing a layer of metal;        -   patterning the metal layer;        -   depositing a first dielectric material having a first            modulus and a first k value;        -   depositing a second dielectric material having a second            modulus higher than the first modulus of the first material            and with a k value lower than the first k value of the first            material; and        -   patterning the first and second dielectric materials and            depositing a via filling metal material into the patterned            areas.

The material according to the invention used for the first dielectriclayer is preferably an organosiloxane material, which has a repeating-M-O-M-O— backbone having a first organic substituent bound to thebackbone, the material having a molecular weight of from 500 to 100,000g/mol, where M is silicon and O is oxygen. The molecular weight is from1500 to 30,000 g/mol, and it preferably exhibits one or several of thefollowing properties:

-   -   a k value of 3.0 or less,    -   a CTE of 25 ppm or less, and    -   a density of 1.2 g/cm³ or more.

The first dielectric material can be an organosiloxane material having acarbon to silicon ratio of 1.5 to 1 or more.

According to another embodiment, the invention provides a method formaking an integrated circuit device, comprising the steps of

-   -   forming transistors on a substrate;    -   depositing one of an electrically insulating or electrically        conducting material;    -   patterning said one of an electrically insulating or        electrically conducting material;    -   depositing the other of the electrically insulating or        electrically conducting material, so as to form a layer over        said transistors having both electrically insulating and        electrically conducting portions;    -   wherein the electrically insulating material has a carbon to        silicon ratio of 1.5 to 1 or more.

Due to the excellent properties of planarization, the patterning stepcan be carried out without a preceding step of chemical mechanicalplanarization. Alternatively, 45% or less of the total thickness of thesecond dielectric material is removed by performing chemical mechanicalplanarization on the second dielectric material.

The organosiloxane material can be deposited by polymerizing a monomerof formula I in a liquid medium formed by a first solvent to form ahydrolyzed product comprising a siloxane material; depositing thehydrolyzed product on the substrate as a thin layer; and curing the thinlayer to form a thin film having a thickness of 0.01 to 10 um.

Whereas one of the dielectric materials comprises a material inaccordance with the present invention, the other material can be aknown, organic, inorganic, or organic/inorganic material, e.g. of thekind discussed above in the introductory portion of the description.

Generally, the organosiloxane material is a spin coated material.

The organosiloxane material is an organic-inorganic and has acoefficient of thermal expansion of 12 to 20 ppm. It can have adielectric constant of 2.7 or less.

Further, the organosiloxane material has a dielectric constant of 3.0 orless. The deposited organosiloxane material has a glass transitiontemperature of 400° C. or more, preferably 450° C. or more, inparticular 500° C. or more.

It is preferred that the organosiloxane layer has a dielectric constantof 2.5 or less. The modulus is 8.0 GPa or more, preferably 10.0 GPa ormore. The density is 1.2 g/cm³ or more, preferably 1.45 g/cm³ or more,in particular 1.65 g/cm³ or more.

In an integrated circuit device according to the invention, theelectrically conductive regions typically comprise aluminum or copper.

Further details of the invention will be discussed in connection withthe following working examples:

EXPERIMENTAL Example 1

Vinyltrichlorosilane, in an amount of 142.2 g (0.880 mol), and 5 ml(5.55 g, 0.048 mol) methyldichlorosilane were introduced into a 500 mlvessel. The solution was heated up to 80° C. and 15 μl H₂PtCl₆/IPAcatalyst solution was added. Exothermic reaction was observedimmediately and heat was switched off. Rest of the methyldichlorosilanewas added in ˜20 ml portions during 30 min so that temperature of thesolution did not raise over 130° C. The total amount ofmethyldichlorosilane was 104.2 g (0.906 mol, 2.9% excess). The solutionwas again heated up to 110° C. and stirred for an hour. The obtainedsolution was distilled. B.p. was 77° C./10 mbar and yield was 188 g(77%). The product, 1-(trichlorosilyl)-2-(methyldichlorosilyl) ethane,was analyzed with GC, ¹³C and ²⁹Si NMR.

The synthesized molecule,1-(trichlorosilyl)-2-(methyldichlorosilyl)ethane, (25.00 g, 0.090 mol)was weighed and dissolved to 100 ml methyl t-butyl ether (MTBE). Thesolution was transferred drop by drop into the solution containing 100ml water and 100 ml MTBE. During addition, solution was mixed vigorouslyand solution temperature was −1 . . . −4° C. The addition time was 20min. After addition, solution was mixed for 20 min at room temperature.

The MTBE phase was allowed to separate and was removed. The aqueousphase was extracted 2 times with 25 ml MTBE. The MTBE phase wasextracted 4 times with 100 ml of water (pH 7) and then filtrated. Theobtained solution was dried into dryness with rotary evaporator (40° C.,<10 mbar) and finally with high vacuum (RT, 1 mbar, ½ h). As a result,12.6 g of low molecular weight material was obtained. The weight averagemolecular weight was 7,650 g/mol and the molecular weight distribution1.28.

The material was dissolved in 50 g MTBE containing 0.146 gtriethylamine. The solution was refluxed for 60 min and cooled to roomtemperature. Then, 20 g of a 2% HCl solution was added and stirred for30 min. The MTBE phase was allowed to separate and was removed. Thesolution was extracted 3 times with 20 ml of water (pH 7). Subsequently,the solution was evaporating into dryness using a rotary evaporator (40°C., <10 mbar) and, finally, with high vacuum (RT, 1 mbar, 1 h). 10.9 gof polymer was obtained (theoretical yield 87%). The weight averagemolecular weight was 15,400 g/mol and the molecular weight distribution1.78.

The invented polymer synthesis and polymerization method describedherein is not limited to above mentioned solvents, catalysts and processconditions, but also similar solvents, catalyst and processingconditions are applicable. However, in course of this invention it isimportant to be able to synthesize and polymerize the final product withgood yield from a single bridged multisilyl monomer without using anycomonomers except for optionally isomeric monomers, which have an equalcarbon number in the linking group even if not in the chain linking thesilicon atoms together.

Comparative Example I

Trichlorosilyl methane (25.00 g, 0.167 mol) was weighed and dissolved in100 ml methyl t-butyl ether (MTBE). The solution was transferred drop bydrop into a solution formed by 150 ml water and 100 ml MTBE. Duringaddition, the solution was vigorously mixed and the temperature of thesolution was maintained at −1 . . . 0° C. Addition time was 10 min.After addition, the solution was mixed for 20 min at room temperature.

The MTBE phase was allowed to separate and was removed. Water phase wasextracted 2 times with 50 ml MTBE. The MTBE phase was extracted 4 timeswith 100 ml of water (pH 7) and then filtrated. Solution was dried intodryness with rotary evaporator (40° C., <10 mbar) and finally with highvacuum (RT, 1 mbar, ½ h). 11.3 g of low molecular weight material wasobtained. Weight average molecular weight was 4 400 g/mol and molecularweight distribution 1.08.

The material was dissolved in 44.7 g MTBE containing 0.045 gtriethylamine. Solution was refluxed for 45 min and cooled to roomtemperature. 22.4 g 2% HCl solution was added and stirred for 30 min.MTBE phase was let to separate and was removed. Solution was extracted 3times with 20 ml of water (pH 7). Solution was dried into dryness withrotary evaporator (40° C., <10 mbar) and finally with high vacuum (RT, 1mbar, 1 h). 10.3 g of polymer was obtained (theoretical yield 92%).Weight average molecular weight was 6 600 g/mol and molecular weightdistribution 1.27.

Both example products (Example I and Comparative Example I) were thendissolved in propylene glycol monomethyl ether acetate (PGMEA) atvarious concentrations to obtain different nominal thicknesses once spincoated on silicon wafer. Still a typical dilution concentration is about400 wt-% of PGMEA solvent against of the final polymer solidconcentration. Furthermore, also other solvent can be used as aprocessing solvent or processing co-solvent such as mesitylene and GPL,but not limited to these. Typically, the materials are filtered aftersolvent concentration formulation with to remove particles out of thespin-on material. Also surfactants and wetting agents may be added priorspin-on processing. By varying the solid content and solvent viscosity(i.e., type of solvent) various thicknesses of above mentioned materialswere able to obtain by processing the materials with spin-on depositionmethod, subjecting them to pre-bake cure and high temperature annealstep. For materials' film level characterization the film thicknessalways exceeded 600 nm when subjected to standard processing conditions,i.e., 2000 rpm spin speed, 150° C. pre-bake step for 5 minutes and hightemperature cure at 450° C. for 1 hour. However, the invented materialis not limited to these process conditions in the course of thisinvention.

Example 2

The present invention also encompasses isomers of1-(trichlorosilyl)-2-(methyldichlorosilyl) ethane. Methyldichlorosilane(14.9 g, 0.130 mol), vinyl trichlorosilane (21.0 g, 0.130 mol) and 100mg tetrakis(triphenylphosphine)palladium were placed in a glass pressuretube and heated to 105° C. After ˜20 minutes, vigorous exothermicreaction too place and the solution turned dark. The content wasdistilled at 74° C./5 mbar to give 32.3 g (0.117 mol, 90%). Puritywas >99% by GC. The resulting monomer was1-(methyldichlorosilyl)-1-(trichlorosilyl)ethane.

Example 3 Alternative Method for Polymer

Examples 1 and 2 describe the synthesis of two monomers, i.e.,1-(trichlorosilyl)-2-(methyldichlorosilyl)ethane and1-(methyldichlorosilyl)-1-(trichlorosilyl)ethane, which can be used asprecursors of polymers.

These isomer compounds, one of which is comprising a linear linker chainand the other a branched linker chain, can be used in any ratio to formthe novel dielectric siloxane polymers according to the presentinvention. Thus, the monomer comprising the linear linker molecule canbe employed at a molar ratios of 1:100 to 100:1, preferably 80:20 to20:80, in particular 60:40 to 40:60, with respect to the correspondingmonomer comprising the branched linker molecule.

Example 4 Alternative Precursor and Polymer

2,2,4,4,4-pentamethoxy-2,4-disilabutane can be used as an alternativeprecursor in the course of this invention. It can be applied alone ortogether above mentioned1-(trichlorosilyl)-2-(methyldichlorosilyl)ethane and1-(methyldichlorosilyl)-1-(trichlorosilyl)ethane precursors. Even2,2,4,4,4-pentamethoxy-2,4-disilabutane is not an isomer for precursorsexplained in Example 1 and 2, it can behaves in similar manner inpolymerization and thus can co-polymerized with monomers explained inExamples 1 and 2 when in 2,2,4,4,4-pentachloro-2,4-disilabutane form.Further it can be homopolymerized or co-polymerized as an alkoxidederivative alone or together with alkoxy forms of precursors in Example1 and Example 2. The synthesis routes for2,2,4,4,4-pentachloro-2,4-disilabutane and2,2,4,4,4-pentamethoxy-2,4-disilabutane are following.

55.10 g (0.337 mol) (ClCH₂)CH₃SiCl₂, 132.13 g (0.975 mol) HSiCl₃ and7.45 g (0.025 mol) Bu₄PCl were added to a stainless steel pressurereactor. Reactor was heated up to 180° C. for 30 min. When pressureformation was not noticed anymore reactor was cooled down to roomtemperature. Solution was distilled yielding 58.85 g (66.5%)MeCl₂Si—CH₂—SiCl₃. B.p. 62° C./10 mbar. 58.85 g (0.224 mol)2,2,4,4,4-pentachloro-2,4-disilabutane was added in small portions to around bottom flask containing 120.0 g (1.131 mol) trimethylorthoformate. 50 mg tetrabutylphosphonium chloride was added as catalystand solution was stirred at 70° C. After 48 hours reaction, no Si—Clbonds remained as observed by shaking a small sample with distilledwater, which remained neutral. Product was purified by distillation,b.p. 80/2 mbar.

In particular, the 2,2,4,4,4-pentachloro-2,4-disilabutane and2,2,4,4,4-pentamethoxy-2,4-disilabutane can be applied to generatefurther rigidity for the dielectric matrix. Therefore, if additionalmechanical rigidity, e.g., modulus and hardness, is required for thedielectric composition, it is then preferred to copolymerize2,2,4,4,4-pentachloro-2,4-disilabutane or2,2,4,4,4-pentamethoxy-2,4-disilabutane with other precursors accordingto formula I, such as with but not limited to1-(trichlorosilyl)-2-(methyldichlorosilyl)ethane per Example I. Theconcentration of 2,2,4,4,4-pentachloro-2,4-disilabutane or2,2,4,4,4-pentamethoxy-2,4-disilabutane can typically be 5-95 mol-%, butmore preferably less 35 mol-%. Due to the similarity and number ofreactive groups and the carbosilane nature of2,2,4,4,4-pentachloro-2,4-disilabutane and2,2,4,4,4-pentamethoxy-2,4-disilabutane they are well co-polymerizabletogether and very homogenous polymers are obtained.

Polymerization can of 1,1,1,3,3-Pentamethoxy-1,3-disilabutane canproceed, for example, in following manner.1,1,1,3,3-Pentamethoxy-1,3-disilabutane by (20 g, 0.083 mol) and acetone(130 mL) were placed in a 250 mL rb flask. Then, 0.018M nitric acid (20mL, 1.110 mol) was added, and the flask was stirred for one hour at rt,after which it was refluxed for 48 hours, followed by 72 hours again atrt. Distilled water was added (50 mL) and the solvents were evaporatedunder reduced pressure until solid content of the solution was 25%,giving polymer-water solution ˜45 mL.

Material Characteristics

Material processed and formed on a substrate as above, was tested todetermine various characteristics of the deposited and fully cured,i.e., cross-linked, material. Properties of the materials, such ascracking threshold, dielectric constant, Young's modulus and hardness,thermal stability, porosity and pore size were also measured.

The dielectric material of this invention can be deposited as very thinlayers from 10 nm up to 10 um (or more). Generally, the material isdeposited at a thickness of from 0.5 to 3 um, preferably from 1 to 5um—though of course the thickness depends upon the actual use of thematerial. The thickness of the deposited layer can be controlled bycontrolling the material viscosity by molecular weight, solvent contentand spinning speed (if deposited by spin on). The material thickness canalso be controlled by adjusting the deposition temperature of both thedeposition solution and the spinner (if spin on deposition). Also,adjusting the solvent vapor pressure and boiling point by selection ofsolvent can affect the thickness of the deposited material. Spincoating, spray coating, dip-coating, meniscus coating, screen printingand “doctor blade” methods can be used to achieve films of varyingthickness. The cracking threshold was studied by spin depositing filmswith various thicknesses up to 3 um (measured after curing) and nocracks were observed in the polymer material of this invention after thecure (this case 1 hour at 450° C.).

Further properties of the densified materials include a density of atleast 1.2 g/cm³, preferably 1.45 g/cm³ or more, 1.60 g/cm³ or more, oreven 1.75 g/cm³ or more. The final material has a glass transitiontemperature, which is higher than 200° C., in particular 400° C. ormore, in particular 500° C. or more. The glass transition temperature(and, naturally, the decomposition temperature) after full cure of thematerial should be higher than processing temperature of thesemiconductor substrate thereafter. At the same time, the dielectricconstant is favorably low—easily 3.0 or less, more typically 2.9 or lessor even 2.5 or less. In addition, the organosiloxane material afterbeing formed has a coefficient of thermal expansion of 12-22 ppm,generally 15-20 ppm.

The polymer organosiloxane material can be suitably deposited such as byspin-on, spray coating, dip coating, or the like. The CTE of the novelpolymer as a thin film is less than 25*10⁻6 l/deg C. The material can becharacterized as being fully dense material which, in the presentcontext means, in particular, that the porosity is low, typically lessthan 10%, preferably less than 5%, in particular less than 3% (byvolume), and the average pore size is less than 3 nm, preferably lessthan 2 nm and in particular less than 1 nm. In course of thisinnovation, the porosity and pore size were tested with VASE (variableangle solvent ellipsometry) using toluene as a test solvent and PALS(positronium annihilation life-time spectroscopy).

In additional, the fully dense dielectric material can be subjected toannealing or a similar pretreatment or post-treatment of heated to thesecond temperature, i.e. the actual curing temperature. The pretreatmentor post-treatment is carried out, e.g., by a process in which thematerial is subjected to UV radiation, DUV radiation, Extreme UVradiation, IR radiation, e-beam radiation, rapid thermal anneal, or acombination thereof. The treated films can be then subjected to curingat an elevated temperature in air, nitrogen, argon, forming gas orvacuum. However, in the course of this invention the polymer explainedin the example I does not require any additional treatment to result inproperties summarized in Table I, but these additional treatments can berather considered to enhance further polymer's film level properties.

The annealed and cured (densified, crosslinked) material can besubjected to deposition of a second layer selected from a metal, abarrier, a liner or an additional dielectric layer.

Mechanical properties, Young's modulus and hardness, were tested interms of nanoindentation (with MTS nanointender) always from filmsthicker than 600 nm in thickness. The Young's modulus of the inventedbridged polyorganosiloxane type material is 8.0 GPa or more, preferably10.0 GPa or more. The film hardness of the invented polyorganosiloxanematerial is 1.0 GPa or more, more preferably 1.5 GPa or more.

The material was also tested for gap filling in terms of coating thepolymer explained in Example I on top of narrow high aspect ratiofeatures on a semiconductor substrate and subjecting the polymer onpre-bake and high temperature treatments, 150° C. for 5 minutes and 450°C. for 60 minutes, respectively. The narrow gap structures down to 35 nmwith aspect ratio of up to 10:1 or more were applied in theseexperiments and a complete gap fill was observed. Also, no densitydifferences were obtained between at top and bottom parts of the gap. Insimilar manner, local and global planarization was tested on isolatedand dense semiconductor structures. The local planarization was observedto be 95% or better and the global planarization was 70% or better.

The shrinkage of the material, in particular after heating to promotecross-linking, is less than 5%, in particular less than 2%.

The electrical properties were tested from MIS (metal insulatorsemiconductor) structure using HP LCR meter and semiconductor analyzerwith a semiconductor electrical test probe station.

The polymer described in Example I according to this invention also isfree of water and silanol after the high temperature cure that wasverified in terms of film level FT-IR spectroscopy. As presented in FIG.1, the FT-IR spectrum does not contain absorption peaks around 3200 cm⁻¹to 3800 cm⁻¹ wherein water and silanol absorption peaks could beobserved, thus evidencing that the film is silanol free.

Properties of the material of the present invention (Example I) andconventional material of Comparative Example I are presented in Table 1.

TABLE 1 COMPARATIVE EXAMPLE I EXAMPLE I Young's modulus 10.5 GPa 4.8 GPaHardness 1.5 Gpa 0.6 GPa Dielectric constant (k) 2.87 2.80 Porosity 1.5%± 1.5% 10% ± 2% Pore size (diameter) 0.9 nm 1.5 nm Cracking threshold3000 nm 1000 nm

It should be pointed out that if precursors according invention as perFormula I are copolymerized with a precursor or similar alkoxyderivative according Comparative Example I, then the material propertiessimilar Example I in Table 1 would not be achievable, but rather besignificantly inferior. Therefore, it preferable to copolymerizeprecursors according to Formula I and as explained in Examples 1 through4.

High Temperature Processing

Because the material of the present invention is stable at very hightemperatures, they are particularly suitable for high temperatureprocessing. In general, the materials can be exposed to temperatures of450° C. or more, or 500° C. or more without degradation. Thus, afterdeposition and curing, one or more following process steps can be at atemperature of 450° C. or more (or even 500° C. or more). As oneexample, in place of a tungsten via, a hot aluminum (also known as“aluminum reflow process”) via fill could be performed followingdeposition of the siloxane material of the invention. Again as anexample, in general, the materials needs to remain unchanged at thesefollowing process steps that may take place even at 500° C. or more forrelatively short period of time, even if the material actual curingprior these following process steps is 450° C. or less.

In a tungsten via process in accordance with the present invention, ascan be seen in FIG. 2 a, after depositing a layer of aluminum, thealuminum is patterned to form “gaps” within the aluminum layer. Intothese gaps is deposited silicon dioxide (by CVD), followed by depositionof the siloxane (SO) material to fill the gaps. Additional silicondioxide is deposited on the siloxane material, followed by chemicalmechanical planarization (CMP). Vias are formed in this layer of silicondioxide by photolithography and etching down to a TiN_(x) stop on thealuminum layer. After ashing, wet cleaning and degassing, a barrierlayer of Ti/TiN_(x) is deposited (this could also be SiOx) within thevia “gaps”, followed by deposition of tungsten (CVD of tungsten from WF₆precursor at 300° C.). Finally the tungsten layer is chemicallymechanically planarized, before proceeding to the next metal layer.

Though this is one suitable method for the materials disclosed herein,due to the lower cost of aluminum as compared to tungsten, and the lowerneed for a CMP step, it is sometimes preferred to form the tungsten viasfrom aluminum—though achieving uniform filling within the vias withaluminum requires a “hot aluminum” step—generally deposition of aluminumat 450° C. or more, or even 500° C. or more if desired. In such a hotaluminum process, as can be seen in FIG. 2 b, first is deposited andpatterned the lower aluminum and TiN_(x) (ARC) layers to form “gaps”.Into these gaps is deposited first a barrier SiO_(x) layer, followed bythe siloxane material of the invention. The spin-on dielectric siloxanematerial of the present invention (SOD) is deposited not only in thepatterned gaps in the aluminum layer (e.g. around 500 nm thick Allayer), but also above the aluminum layer (e.g. 300 nm higher). On topof the SOD material (this could also be deposited by CVD) is deposited alayer of SiO_(x) by CVD (more particularly, this can be TEOS—tetra ethylortho silicate/silicon tetra ethoxide). Without performing a chemicalmechanical planarizing step (or by removing through planarization

45% or less of the thickness of this SiO_(x)/TEOS layer—or generally 35%or even 25% or less), via lithography is performed to form vias down tothe aluminum layer. After ashing, wet cleaning and degassing, a barrierlayer is deposited (e.g. Ti/TiN_(x)), followed by deposition of the hotaluminum at a temperature of 450° C. or more, often 500° C. or more. Thealuminum is chemically mechanically planarized prior to proceeding tothe next metal layer. Desirably, the siloxane material of the presentinvention has no detectable change in k value or modulus (or nosubstantial change that affects the ability of the siloxane material tobe used in such processes), nor does the siloxane material outgas, evenif exposed to temperatures of 450° C. or more, or 500° C. or more (oreven 525° C. or more depending upon the length of time of suchexposure).

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. Obviously, many modifications and variations will be apparentto practitioners skilled in this art. It is intended that the scope ofthe invention be defined by the following claims and their equivalents.

Due to the thermal stability and excellent gap fill of the inventedmaterial, it can be also utilized as dielectric material in PMD(pre-metal dielectric) and STI (Shallow Trench Isolation) applications.Dielectrics for these applications are typically deposited with HD-CVD(high density chemical vapor deposition) process. However, HDP-CVDcannot make good and uniform gap fill for very narrow and high aspectratio structures that specially needed in PMD and STI applications.Therefore, the invented material as explained earlier has competitiveadvantages in performance and cost over traditional processes.

1. A method for making an integrated circuit device, comprising: forminga plurality of transistors on a semiconductor substrate; formingmultilayer interconnects by: depositing a layer of metal; patterning themetal layer; depositing a first dielectric material; depositing a seconddielectric material; patterning the first and second dielectricmaterials and depositing a via filling metal material into the patternedareas; wherein the first dielectric material is an organosiloxanematerial having a carbon to silicon ratio of 1.5 to 1 or more.
 2. Amethod for making an integrated circuit device, comprising: formingtransistors on a substrate; depositing one of an electrically insulatingor electrically conducting material; patterning said one of anelectrically insulating or electrically conducting material; depositingthe other of the electrically insulating or electrically conductingmaterial, so as to form a layer over said transistors having bothelectrically insulating and electrically conducting portions; whereinthe electrically insulating material has a carbon to silicon ratio of1.5 to 1 or more.